Enhanced Oil Recovery (abbreviated EOR) refers to techniques for increasing the amount of unrefined petroleum, or crude oil that may be extracted from an oil reservoir (e.g. an oil field). Using EOR, 40-60% of the reservoir's original oil can typically be extracted compared with only 20-40% using primary and secondary recovery (e.g. by water injection or natural gas injection). Enhanced oil recovery may also be referred to as improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery).
Enhanced oil recovery may be achieved by a variety of methods including miscible gas injection (which includes carbon dioxide flooding), chemical injection (which includes polymer flooding, alkaline flooding and surfactant flooding), microbial injection, or thermal recovery (which includes cyclic steam, steam flooding, and fire flooding). The injection of various chemicals, usually as dilute aqueous solutions, has been used to improve oil recovery. Injection of alkaline or caustic solutions into reservoirs with oil that has organic acids or acid precursors naturally occurring in the oil will result in the production of soap (i.e. in situ generated soap) that may lower the interfacial tension enough to increase production. Injection of a dilute solution of a water soluble polymer to increase the viscosity of the injected water can increase the amount of oil recovered in some formations. Dilute solutions of surfactants such as petroleum sulfonates may be injected to lower the interfacial tension or capillary pressure that impedes oil droplets from moving through a reservoir. Special formulations of oil, water and surfactant microemulsions have also proven useful. Such formulations may further include co-solvent compounds which have the capability of increasing the solubility of the solutes in the presence of oil and are able to decrease the viscosity of an emulsion. Application of these methods is usually limited by the cost of the chemicals and their adsorption and loss onto the rock of the oil containing formation.
Therefore, there is a need in the art for cost effective methods for enhanced oil recovery using chemical injection. Provided herein are methods and compositions addressing these and other needs in the art.